The invention relates to a process for copolymerizing alpha-olefins and divinylbenzene, which process utilizes certain metallocene catalysts to produce alpha-olefin/divinylbenzene copolymers having a linear copolymer structure and narrow molecular weight and composition distributions, and to a process for preparing polyolefin graft copolymers containing polyolefin backbone and pendant polymer side chains derived from both chain and step growth polymerization reactions. The process for preparing the graft copolymers includes functionalization and graft copolymerization reactions utilizing the linear copolymers of alpha-olefins and divinylbenzene, which have been prepared using certain metallocene catalysts.
The invention also relates to the linear alpha-olefin/divinylbenzene copolymers and to the polyolefin graft copolymers that are prepared in accordance with the processes of this invention.
Although useful in many commercial applications, polyolefin homopolymers, such as high density polyethylene (HDPE) and isotactic polypropylene (i-PP), suffer poor interaction with other materials. The inert nature of polyolefins significantly limits their end uses, particularly those in which adhesion, dyeability, paintability, printability or compatibility with other functional polymers is paramount.
Unfortunately, because of their inert nature and crystallinity, polyolefins have been among the more difficult materials to chemically modify by means of post-polymerization processes. In many cases, the post-polymerization reactions result in serious side reactions, such as degradation and crosslinking reactions. Although the direct copolymerization is the most effective route to functionalize polyolefins, such direct processes usually are laden with difficulties and limitations.
Only the transition metal coordination catalysts (Ziegler-Natta and metallocene catalysts) can be used in the preparation of linear polyolefins, and it normally is difficult to incorporate functional group-containing monomers into the polyolefins by using the early transition metal catalysts due to catalyst poisoning (see J. Boor, Jr., Ziegler-Natta Catalysts and Polymerizations, Academic Press, New York, 1979). The Lewis acid components (Ti, V, Zr and Al) of the catalyst will tend to complex with nonbonded electron pairs on N, O, and X (halides) of functional monomers in preference to complexation with the xcfx80-electrons of the double bonds. The net result is the deactivation of the active sites by formation of stable complexes between catalysts and functional groups, thus inhibiting polymerization.
In several prior art disclosures, it has been taught to prepare reactive polyolefin copolymers containing either borane (see U.S. Pat. Nos. 4,734,472; 4,751,276; 4,812,529; 4,877,846) or p-methylstyrene (see U.S. Pat. Nos. 5,543,484; 5,866,659 and 6,015,862; and J. Polym. Sci. Polym Chem., 36, 1017, 1998; J. Polym. Sci. Polym Chem., 37, 2795, 1999; and Macromolecules, 31, 2028, 1998) reactive comonomer units. The chemistry disclosed in this prior art involves the direct copolymerization of alpha-olefins and organoborane-substituted monomers and p-methylstyrene, respectively, with Ziegler-Natta and metallocene catalysts. The homo- and copolymers containing reactive borane or p-methylstyrene groups are very useful intermediates for preparing a series of functionalized polyolefins. Many new functionized polyolefins with various molecular architectures have been obtained based on this chemistry. In addition, it has been demonstrated that polar groups can improve the adhesion of polyolefins to many substrates, such as metals and glass (see Chung et al, J. Thermoplastic Composite Materials, 6, 18, 1993 and Polymer, 35, 2980, 1994). The application of both borane-containing polymers and p-methylstyrene-containing polymers also has been extended to the preparation of polyolefin graft copolymers, which involves free radical (see U.S. Pat. Nos. 5,286,800 and 5,401,805; Chung et al, Macromolecules, 26, 3467, 1993; and Chung et al, Macromolecules, 32, 2525, 1999) and anionic graft-from reactions (see Chung et al, Macromolecules, 30, 1272, 1997), respectively. In polymer blends, compatibility of the polymers can be improved by adding a suitable polyolefin graft copolymer which reduces the domain sizes and increases the interfacial interaction between domains (see Chung et al, Macromolecules, 26, 3467, 1993; Macromolecules, 27, 1313, 1994).
Another approach toward preparing functionalized polyolefins is the preparation of unsaturated polyolefin copolymers containing pending unsaturated side chains, which are reactive in subsequent chemical functionalization reactions. In general, the transition metal (Ziegler-Natta and metallocene catalysts) copolymerization of alpha-olefin and diene monomer is a great concern with many potential side reactions. The diene monomer, containing two reactive sites, potentially may engage in a double addition reaction to form copolymers having long branching side chains or even three dimensional network (crosslinked) structures. Most of linear diene-containing copolymers that have been reported involve the use of asymmetric dienes (see U.S. Pat. Nos. 3,658,770; 4,680,318; and 4,366,296) which contain only one polymerizable olefin unit, either an alpha-olefin or a constrained cycloolefin moiety, to prevent the formation of crosslinked (unprocessible) products. The asymetric dienes include those containing an alpha-olefin unit and an internal olefin unit, such as 1,4-hexadiene and methyl-1,4-hexadiene, and those containing a constrained cycloolefin unit and a linear olefin unit, such as 2-methylene-5-norborene, 5-vinyl-2-norborene and dicyclopentadiene. Several unsaturated polyolefins have been reported, including unsaturated polyethylene copolymers (Marathe et al. Macromolecules, 27, 1083, 1994), polypropylene copolymers (Kitagawa et al., Polymer Bulletin, 10, 109, 1983) and ethylene-propylene terpolymers (VerStrate et al, Encyclopedia of Polym. Sci. and Eng., 6, 522, 1986). Recently, Machida et al. (JP 05-194665 and JP 05-194666) also reported the copolymerization of alpha-olefins and asymetric styrenic diene comonomers, such as p-(3-butenyl)styrene, to produce linear copolymers using Ziegler-Natta heterogeneous catalysts.
Alpha-olefin polymerization involving symmetric alpha,omega-diene comonomers in which both double bonds are terminal alpha-olefins are very limited. One such polymerization, which involved the copolymerization of alpha-olefin and 1,3-butadiene (Bruzzone et al., Makromol. Chem., 179, 2173, 1978; Cucinella et al., European Polym. J., 12, 65, 1976), resulted in copolymers where the butadiene units in the copolymer were mostly in the trans-1,4-configuration. In other words, both alpha-olefins in the butadiene monomer were engaged in the polymerization reaction. Some diene comonomers having a long spacer between two terminal olefins, including C8-C14 aliphatic alpha,omega-dienes, such as 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene and 1,13-tetradecadiene (see U.S. Pat. Nos. 4,551,503; 4,340,705; and 5,504,171), were found to be more selective so as to engage only one olefin group in the heterogeneous Ziegler-Natta copolymerization reaction. The resulting polyolefin copolymers have pending alpha-olefin groups located along the polymer chain.
Incorporating a divinylbenzene comonomer into a linear polyolefin would result in polyolefin copolymers containing pending styrene groups, as illustrated, for example, in Formula (I) where the divinylbenzene may comprise 1,2-divinylbenzene, 1,3-divinylbenzene, 1,4-divinylbenzene or mixtures thereof. Such copolymers could be used as versatile precursors for a broad range of polyolefin structures, including the polyolefin graft copolymers containing polyolefin backbone and other polymer side chains. However, it is very difficult to prepare linear polyolefin copolymers having a well-defined molecular structure, as illustrated in Formula (I), due to potential branching and crosslinking reactions, resulting from the difuntional nature of the divinylbenzene comonomer(s).
The transition metal copolymerization of styrenic monomers and alpha-olefins usually is very difficult to accomplish (see Seppala et al., Macromolecules, 27, 3136, 1994 and Soga et al., Macromolecules, 22, 2875, 1989). This is especially true when using stereospecific heterogeneous Ziegler-Natta catalysts having multiple active sites, since the reactivity of monomer is sterically controlled, i.e., the larger the size of the monomer, the lower the reactivity; and those few styrenic copolymers that are known tend to be very inhomogeneous (Mijatake, et al., Makromol. Chem. Macromol. Symp., 66, 203, 1993; Aaltonen, et al., Macromolecules, 27, 3136, 1994; and U.S. Pat. No. 5,543,484) and to have broad molecular weight and composition distributions (and even to include some homopolymer).
The copolymerization of alpha-olefin and divinylbenzene by Ziegler-Natta catalysts has been disclosed (Yokoyama, et al., Eur. Pat. Appl. 88310305.3 and Yoshitake, et al., JP 62-241907). It also has been disclosed that the resulting copolymers can be used in the preparation of polyolefin graft copolymers (Yokoyama, et al., JP 03-255114; Tomita, et al., JP 08-003231, JP 08-003232 and JP 05-017539). However, as expected, the known copolymers of divinylbenzene and alpha-olefins, especially ethylene and propylene, are very inhomogeneous, showing broad composition and molecular weight distribution (Mw/Mn greater than 6), due to multiple active sites and sterically-controlled monomer reactivity. Also, the extent of side reactions has not been reported, possibly because it may be very difficult to determine the extent of side reactions due to the very low concentration of divinylbenezene in the copolymer products. The divinylbenzene content in the ethylene and propylene copolymers is below 0.3 mole % (1 wt %) and the overall divinylbenzene conversion is only few % in each case. In general, the catalyst activity is inversely proportional to the concentration of divinylbenzene in the monomer feed.
Machida, et al. (U.S. Pat. No. 5,608,009) also reported the copolymerization reaction of ethylene and diene comonomers (including diene compounds having aromatic rings including divinylbenzene and others) by using metallocene catalysts. The diene-containing copolymers were used as intermediates in the preparation of graft copolymers, including long chain branching polyolefins. In general, the alpha-olefin/divinylbenzene copolymers reported by Machida, et al. were complex and had ill-defined molecular structures. Moreover, Machida, et al. failed to identify the reaction conditions that are necessary to prepare copolymers having a linear molecular structure and narrow composition and molecular weight distributions (as discussed in Column 16, lines 41-45, the olefin copolymers obtained by Machida, et al. were long-branched copolymers). The disclosed examples of copolymerization reactions between ethylene and divinylbenzene involved using dicyclopentadienylzirconium dichloride (in Example 1) and cyclopentadienylzirconium trimethoxide (in Example 3) as the catalyst system. The molecular structures of the resulting ethylene/divinylbenzene copolymers were complex and the copolymers were characterized by a low molecular weight (Mw=5,670 in Example 1 and Mw=14,500 in Example 3) and broad molecular weight distributions (Mw/Mn=6.6 in Example 1 and Mw/Mn=23 in Example 3). The inhomogeneous and non-linear copolymer structures were clearly revealed by the ratio of unsaturation/divinylbenzene (TUS/DOU) in the copolymers, the ratios being 0.71 (in Example 1) and 7.55 (in Example 3) using dicyclopentadienylzirconium dichloride and cyclopentadienyltitanium trimethoxide, respectively.
It is well known that metallocene polymerization results in polymers that are terminated mainly by beta-hydride elimination to form an unsaturated site at the chain end. Accordingly, it would be logical that the TUS/DOU ratio should be near unity for a linear copolymer of the type contemplated by the present invention, as illustrated in Formula (I). Thus, for a linear polymer, it would be expected that as the polymerization reaction continues and as the molecular weight increases (and as divinylbenzene units become incorporated into the copolymer), the contribution of chain end unsaturation to the TUS/DOU ratio would be very small. In other words, the TUS/DOU ratio should remain at or very close to unity. Similarly, it would be logical to assume that a copolymer that is characterized by a TUS/DOU ratio that deviates substantially from unity would be a non-linear, inhomogeneous copolymer containing many chain ends. For the known ethylene/divinylbenzene copolymers that were prepared using dicyclopentadienylzirconium dichloride (Example 1, above), the ratio of TUS/DOU=0.71 strongly suggests that a good portion of the divinylbenzene units that were incorporated into the copolymer had undergone double addition reactions at both vinyl groups to produce a polymer having a long-chain branching structure. Overall, the prior disclosures fail to identify the reaction conditions, especially the catalyst systems, which are necessary to prepare linear alpha-olefin/divinylbenzene copolymers having narrow composition and molecular weight distributions.
Machida, et al. (Eur. Pat. Appl. 93103181.9 (Pub. No. 0 559 108 A1)) also reported the application of the copolymerization adducts of alpha-olefin and diolefin comonomers (including divinylbenzene) for the preparation of graft copolymer containing syndiotactic polystyrene (s-PS) side chains. The results clearly demonstrated the disadvantages of using divinylbenzene as the diolefin unit under their reaction conditions. The problems include the formation of crosslinked product, difficulty in assuring sufficient reactivity and monomers remaining unreacted. In fact, the graft copolymers with much better quality were prepared by using other diolefin monomers.
In general, the advances in metallocene catalysts (see U.S. Pat. Nos. 4,542,199; 4,530,914; 4,665,047; 4,752,597; 5,026,798 and 5,272,236) provide an excellent opportunity for chemists to prepare new polyolefin polymers. With well-defined (single-site) catalysts and a designed active site geometry, monomer insertion can be controlled effectively, both kinetically and sterically, during a polymerization process. This is especially important for copolymerization reactions for producing copolymers having a relatively well-defined molecular structure. Several prior publications have disclosed the use of metallocene catalysts having a constrained ligand geometry for producing narrow composition distribution and narrow molecular weight distribution linear low density polyethylene (LLDPE).
For copolymerization reactions, use of a relatively opened active site metallocene catalyst provides essentially equal access for both comonomers, and the incorporation of higher molecular weight olefin comonomer is significantly higher than for those copolymers obtained from traditional Ziegler-Natta catalysts. In fact, some metallocene catalysts with constrained ligand geometry and opened active site have been shown to be effective for incorporation of styrenic monomers in polyolefin copolymers, including poly(ethylene-co-styrene) (U.S. Pat. No. 5,703,187), poly(ethylene-co-p-methylstyrene), poly(ethylene-ter-propylene-ter-p-methylstyrene) and poly(ethylene-ter-1-octene-ter-p-methylstyrene) (U.S. Pat. No. 5,543,484, and J. Polym. Sci. Polym Chem., 36, 1017, 1998, Macromolecules, 31, 2028, 1998).
The invention relates to copolymers containing alpha-olefin and divinylbenzene comonomer units, which copolymers have a linear molecular structure and are characterized by a mole ratio of unsaturation/divinylbenzene (TUS/DOU) near unity. The copolymers are also characterized by a narrow molecular weight distribution and a narrow composition distribution, and may be represented by the following structural Formula (I): 
in which R is a linear or branched alkyl group, or a cyclic aliphatic or aromatic group, x represents the mole % of ethylene units in the copolymer, y represents the mole % of alpha-olefin comonomer units in the copolymer, and z represents the mole % divinylbenzene units in the copolymer. Preferably, R is a C1 to C10 linear or branched alkyl group or a C6 to C10 substituted or unsubstituted aromatic group, and most preferably, R is C1 to C6 alkyl group or substituted or unsubstituted C6 aromatic group. The value of x may vary from 0% to about 99.9%, as may the value of y; provided, however, that the combined value of alpha-olefin mole % (x+y) in the copolymer is from about 50 to 99.9%. Preferably, x+y is between 85 to 99.9%, and most preferably x+y is from 95 to 99.9%. The sum of x, y and z (mole % of divinylbenzene) is 100%. The mole ratio of unsaturation/divinylbenzene (TUS/DOU) in the copolymers is near unity, typically from 0.8 to 1.1. Preferably, the TUS/DOU ratio is from 0.9 to 1, and most preferably ratio is from 0.95 to 1. The copolymers of this invention have a number average molecular weight (Mn) of at least about 1,000, and preferably at least about 10,000. The copolymers also preferably have a molecular weight distribution (ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), or Mw/Mn) of less than about 4. Preferably, Mw/Mn is less than 3. Furthermore, the copolymers have narrow composition distribution with the incorporated divinylbenzene units being distributed homogeneously along all of the polymer chains.
The invention also relates to a polymerization process for producing alpha-olefin/divinylbenzene copolymers (I) having a linear molecular structure, a mole ratio of unsaturation/divinylbenzene (TUS/DOU) near unity, and narrow molecular weight and composition distributions. The process involves contacting the alpha-olefin and divinylbenzene comonomers under copolymerization reaction conditions in the presence of a single-site metallocene catalyst having substituted covalently-bridged ring ligands and a specific opening at the metal active site, as illustrated below: xe2x80x83xcfx86=∠Lxe2x88x92Mxe2x88x92Lxe2x80x2
where M is a transition metal of group 3 or group 4 of the Periodic Table of the Elements; L and Lxe2x80x2, independently, are selected from xe2x80x94NRxe2x80x2xe2x80x94, xe2x80x94PRxe2x80x2xe2x80x94, cyclopentadienyl or substituted cyclopentadienyl groups bound in an xcex75 bonding mode to M, wherein at least one of L and Lxe2x80x2 is a cyclopentadienyl or a substituted cyclopentadienyl group, and wherein each occurrence of Rxe2x80x2, independently, is selected from the group consisting of hydrogen, alkyl, aryl, silyl, halogenated alkyl, halogenated aryl, and mixtures thereof, Y is a moiety selected from xe2x80x94SiRxe2x80x22xe2x80x94, xe2x80x94CRxe2x80x22xe2x80x94, and xe2x80x94CRxe2x80x22xe2x80x94CRxe2x80x22xe2x80x94; X is selected from hydride, halo, alkyl, aryl, aryloxy, and alkoxy; and n is 0, 1 or 2; and the angle, "PHgr", formed at the metal center between two L and Lxe2x80x2 ligands, such as the centroid of two cyclopentadienyl or substituted cyclopentadienyl groups, is from 135xc2x0 to 105xc2x0. Preferably, the value of "PHgr" is from 130xc2x0 to 115xc2x0, and most preferably, the value of "PHgr" is from 128xc2x0 to 120xc2x0.
The constrained ligand geometry associated with the covalently-bridged ligands results in a specific space opening at the metal active site, which provides the selective reaction with only one of the two vinyl groups in divinylbenzene during the copolymerization between alpha-olefins and divinylbenzene. In other words, the catalysts contemplated for use in the present invention can effectively incorporate divinylbenzene into the copolymer chain through single enchainment, but show poor reactivity to the styrenic units already existing in the copolymer (I).
The metallocene catalysts contemplated for use in this invention may be used as such. However, as is known, the catalysts may be used in conjunction with a cocatalyst or activator, such as aluminoxane and tris(pentafluorophenyl)borane.
In accordance with another embodiment of the invention, functionalized polyolefins and graft copolymers are prepared by chemically reacting the pending styrene units in the alpha-olefin/divinylbenzene copolymers (I). The resulting functionalized polyolefins and graft copolymer may be illustrated in Formula (II), below 
in which R is defined above in connection with Formula (I). G and Gxe2x80x2, independently, are selected from xe2x80x94H, xe2x80x94OH, epoxy, xe2x80x94NH2, xe2x80x94COOH, anhydride, xe2x80x94Cl, xe2x80x94Br, xe2x80x94M, xe2x80x94COOM (M=metals, e.g. Li, Na, K and Ca) or a polymer chain having a molecular weight of at least about 500, which can be derived from both step and chain polymerization reactions; x and y are as previously defined in connection with Formula (I); m is the mole % of divinylbenzene units remaining in the functionalized copolymer; n is the mole % of functionalized styrenic units and is at least 0.1%; and the sum of x, y, m and n is 100%. As indicated in connection with Formula (I), the combined alpha-olefin mole % (x+y) in the functionalized copolymer (Formula (II)) is from about 50 to 99.09%. Preferably, x+y is between 85 to 99.9%, and most preferably x+y is from 95 to 99.9%. The sum of x, y, m and n is 100%, and n is at least 0.05%. The backbone polymer chain has a number average molecular weight (Mn) of at least about 1,000, and preferably at least about 10,000.Typically, the backbone polymer chain has a number average molecular weight (Mn) of from about 20,000 to about 200,000.
In one aspect of the invention, applicants have discovered the reaction processes for producing functionalized polyolefins and graft copolymers (II) by the chemical reactions of pending styrene units in alpha-olefin/divinylbenzene copolymers (I), which have a linear molecular structure and narrow molecular weight and composition distributions. The linear copolymers have monomer units which may be represented by the structural formula, 
in which R is an alkyl group, or a cyclic aliphatic or aromatic group. Preferably, R is C1 to C10 linear or branched alkyl group, or a C6 to C10 substituted or unsubstituted aromatic group, and most preferably, a C1 to C6 alkyl group or a substituted or unsubstituted C6 aromatic group. In the copolymer composition, the combined alpha-olefin mole % (x+y) is from about 50 to 99.9 mole %. Preferably, x+y is from 85 to 99.9 mole %, and most preferably x+y is from 95 to 99.9 mole %. The sum of x, y and z (mole % of divinylbenzene) is 100%. The copolymer I has a number average molecular weight (Mn) of at least about 1,000, and preferably at least about 10,000 (typically from at least about 20,000). The copolymers also preferably have a ratio of weight average molecular weight (Mw) to number average molecular weight, or Mw/Mn, less than about 4. Preferably, Mw/Mn is less than 3. Furthermore, the copolymers have narrow composition distribution with the incorporated divinylbenzene units homogeneously distributed along all the polymer chains.
The pendant styrene groups in the polyolefin copolymer (I) are very versatile, and can be converted to functional (polar) groups, such as xe2x80x94OH, epoxy, xe2x80x94NH2, xe2x80x94COOH, anhydride, xe2x80x94Cl, xe2x80x94Br, xe2x80x94M, xe2x80x94COOM (M=metal, e.g. Li, Na, K and Ca), by conventional organic olefinic chemistry. The resulting converted copolymer contains pendant functional groups, which can further serve as the coupling sites for reacting with a polymer having a terminal reactive group to form a graft copolymer (II). With the careful selection of a coupling pair, a coupling reaction can take place effectively in solution or melt. A coupling reaction also can be accomplished during a reactive extrusion process. Furthermore, it is very convenient to prepare graft copolymer (II) by using the pendant styrene groups in the polyolefin copolymer (I) as a monomer unit in a subsequent polymerization process. In other words, a second copolymerization reaction involving copolymer (I) and olefinic monomers can take place via either a graft-onto or a graft-through process to produce graft copolymer (II), containing polyolefin backbone and several pendant polymer side chains.
As illustrated in Formulas (I) and (II), the incorporated divinylbenzene-derived units are derived from 1,4-divinylbenzene. However, it will be appreciated that the incorporated divinylbenzene-derived units could be derived from 1,3-divinylbenzene or, possibly, from 1,2-divinylbenzene, or from mixtures of two or more of 1,4-divinylbenzene, 1,3-divinylbenzene and 1,2-divinylbenzene. In fact, the divinylbenzene comonomer that would used to prepare the linear copolymers of the present invention typically would comprise mixtures of 1,4-divinylbenzene and 1,3-divinylbenzene, possibly with some small amount of 1,2-divinylbenzene. Commercially available divinylbenzene compositions typically comprise a mixture of 1,3- and 1,4-divinylbenzene in a weight ratio of from about 1:1 to about 1:4, e.g., about 1:2.5. Accordingly, unless specifically stated otherwise, the term xe2x80x9cdivinylbenzenexe2x80x9d is used in this specification and claims to include 1,4-divinylbenzene, individually, 1,3-divinylbenzene, individually, as well as mixtures of 1,4- and 1,3-divinylbenzene or mixtures of 1,4-, 1,3- and 1,2-divinylbenzene. Similarly, unless specifically stated otherwise, when divinylbenzene-derived units are illustrated in this specification and claims, as in Formulas (I) and (II), as being derived from 1,4-divinylbenzene, the illustration is meant to include units derived from 1,4-divinylbenzene, individually, from 1,3-divinylbenzene, individually, as well as units derived from mixtures of 1,4- and 1,3-divinylbenzene and from 1,4-, 1,3-and 1,2-divinylbenzene. In preferred aspects of the invention, the term xe2x80x9cdivinylbenzenexe2x80x9d is used to describe 1,4-divinylbenzene or mixtures of 1,4- and 1,3-divinylbenzene.
This invention is based on the discovery that with certain metallocene catalysts the effective copolymerization reaction of alpha-olefin and divinylbenzene can take place to produce alpha-olefin/divinylbenzene copolymers having a linear copolymer structure. The unsaturation/divinylbenzene (TUS/DOU) ratio in the copolymers (I) is near unity, the copolymers do not contain any substantial branching or crosslinking (no branching or crosslinked structures were detected in the copolymers that were produced), and the copolymers are completely soluble and processible. The copolymers comprise the direct copolymerization product of alpha-olefin having from 2 to 12 carbon atoms and divinylbenzene, and are high molecular weight linear polymers having a substantially homogeneous molecular structure, i.e. narrow molecular weight and composition distributions. The copolymers may be illustrated by the following formula: 
in which R is a linear or branched alkyl group or a cyclic aliphatic or aromatic group. Preferably, R is C1 to C10 linear and branched alkyl or a C6 to C10 substituted or unsubstituted aromatic group, and most preferably R is C1 to C10 alkyl group or a C6 substituted or unsubstituted aromatic group, e.g. phenyl or alkyl-substituted phenyl.
The TUS/DOU ratio is near unity, and typically is between 0.8 and 1.1. Preferably, the TUS/DOU ratio is between 0.9 and 1, and most preferably ratio is between 0.95 and 1. In the formula (I), x represents the mole % of ethylene units in the copolymer, y represents the mole % of alpha-olefin comonomer units in the copolymer, and z represents the mole % divinylbenzene units in the copolymer. The value of x may vary from 0% to about 99.9%, as may the value of y; provided, however, that the combined value of alpha-olefin mole % (x+y) in the copolymer is from about 50 to 99.9%. Typically, one of x or y is greater than 40 mole %, and in many preferable cases, one of x or y is greater than 60 mole %. Preferably, x+y is from 85 to 99.9%, and most preferably x+y is from 95 and 99.9%. The sum of x, y and z (mole % of divinylbenzene) is 100%.
The copolymers of this invention have a number average molecular weight (Mn) of at least about 1,000, and preferably at least about 10,000. Typically, the copolymers have a number average molecular weight of from about 20,000 up to about 200,000 The copolymers also preferably have a molecular weight distribution (ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), or Mw/Mn) of less than about 4. Preferably, Mw/Mn is less than 3, for example, from about 1.9 to about 2.8. Furthermore, the copolymers0 have narrow composition distribution with the incorporated divinylbenzene units homogeneously distributed along all the polymer chains.
As disclosed herein, and as illustrated in the Tables, the copolymerization of alpha-olefin (such as ethylene and propylene) and divinylbenzene using a metallocene (single-site) coordination catalyst is greatly dependent on the geometry of the active site. The metallocene catalysts having non-bridged ligand geometry, such as dicyclopentadienylzirconium dichloride/methylaluminoxane, have a very limited opening at the active metal site (xcfx86 greater than 135xc2x0) and greatly favor the incorporation of small size monomers. Therefore, only very low % of divinylbenzene can be incorporated into the copolymers having ethylene and propylene monomer units when using a non-bridged metallocene as the catalyst. On the other hand, metallocene catalysts having highly constrained ligand geometry, and which have active sites that are very opened (xcfx86 less than 105xc2x0), are capable of copolymerizing alpha-olefin(s) and divinylbenzene. However, when using metallocene catalysts having such very open active sites (i.e. xcfx86 less than 105xc2x0) double enchainment of both vinyl groups in divinylbenzene comonomer is highly likely to occur during the copolymerization process, which results in copolymers having branched or/and crosslinked structures.
Thus, the invention involves the use of metallocene catalysts having a specific ligand geometry and a specified opening at the active metal site, which can effectively and selectively react with only one of the two vinyl groups in the divinylbenzene comonomer during alpha-olefin and divinylbenzene copolymerization reactions. The specific single-site metallocene catalysts contemplated for use in the present invention have substituted covalently-bridged ring ligands are illustrated below. xe2x80x83xcfx86=∠Lxe2x88x92Mxe2x88x92Lxe2x80x2
wherein M is a transition metal of group 3 or 4 of the Periodic Table of the Elements; L and Lxe2x80x2, independently, are selected from xe2x80x94NRxe2x80x2xe2x80x94, xe2x80x94PRxe2x80x2xe2x80x94, cyclopentadienyl or substituted cyclopentadienyl groups bound in an xcex75 bonding mode to M, wherein at least one of L and Lxe2x80x2 is a cyclopentadienyl or substituted cyclopentadienyl group, and wherein each occurrence of Rxe2x80x2, independently, is selected from the group consisting of hydrogen, alkyl, aryl, silyl, halogenated alkyl, halogenated aryl, and mixtures thereof; Y is a moiety selected from xe2x80x94SiRxe2x80x22xe2x80x94, xe2x80x94CRxe2x80x22xe2x80x94, and xe2x80x94CRxe2x80x22xe2x80x94CRxe2x80x22xe2x80x94, where Rxe2x80x2 is as previously defined; X is selected from hydride, halo, alkyl, aryl, aryloxy, and alkoxy; and n is 0, 1 or 2.
The catalysts to be used in this invention are further defined by a geometry angle, "PHgr", formed at the metal center between two L and Lxe2x80x2 ligands, such as the centroid of two cyclopentadienyl or substituted cyclopentadienyl groups. The value of "PHgr" must be from 135xc2x0 to 105xc2x0. Preferably, the value of "PHgr" is from 130xc2x0 to 115xc2x0, and most preferably, the value of "PHgr" is from 128xc2x0 to 120xc2x0.
Catalysts that may be used in the present invention include, for example, ethylenebis (indenyl) zirconium dichloride, ethylenebis (tetrahydroindenyl) zirconium dichloride, ethylenebis (indenyl) dimethylzirconium, and the like. The amount of such catalysts employed will depend on the desired molecular weight and the desired molecular weight distribution of the copolymer being produced, but will generally range from about 20 ppm to 1 wt. %, and preferably from about 0.001 to 0.2 wt. %, based upon the total amount of monomer to be polymerized therein.
Metallocene catalysts are known to be activated with a co-catalyst, which typically is a Bronsted acid salt with a noncoordinating anion. Accordingly, it is preferred to use the metallocene catalysts in combination with a co-catalyst. Non-limiting examples of co-catalysts that are contemplated for use in this invention include aluminoxane, tris(pentafluorophenyl)borane, trimethylammonium tetraphenylborate, triethylammonium tetrakis(pentafluorophenyl)borate, and the like.
The constrained ligand geometry associated to the covalently-bridged ligands results in the specific space opening at the metal active site, which provides for the selective reaction with only one of the two vinyl groups in divinylbenzene during the copolymerization between alpha-olefins and divinylbenzene. In other words, the catalyst can effectively incorporate divinylbenzene into polymer through single enchainment, but shows poor reactivity to the styrenic units already existing in the copolymer (I). The selective copolymerization of divinylbenzene is illustrated below: 
Since only one vinyl group in the divinylbenzene monomer is involved in the copolymerization reaction, the side reactions (described in the prior art) involving pendant styrene vinyl groups in the copolymer (I) and producing branched polymers or crosslinked polymers can be avoided. The resulting copolymer (I) is a linear soluble polymer having an unsaturation/divinylbenzene (TUS/DOU) ratio near unity, e.g., between about 0.8 and 1.1. In addition, the catalytic sites having favorable divinylbenzene incorporation (involving only a single vinyl group) results in linear copolymers having a broad range of divinylbenzene contents and narrow molecular weight and composition distributions.
Suitable diluents for the monomers, catalyst components and polymeric reaction products include the general group of aliphatic and aromatic hydrocarbons, used singly or in a mixture, such as propane, butane, pentane, cyclopentane, hexane, toluene, heptane, isooctane or the like. The processes of the present invention can be carried out in the form of a slurry of polymer formed in the diluents employed, or as a homogeneous solution process, depending on the alpha-olefin used. The use of a slurry process is, however, preferred, since in that case lower viscosity mixtures are produced in the reactor, and slurry concentrations up to 40 wt. % of polymer are possible. At higher slurry concentrations it is possible to operate a more efficient process in which it is necessary to recycle less of the reactants and diluent for each unit of polymer produced.
In general, the polymerization reactions of the present invention are carried out by mixing divinylbenzene and alpha-olefin (ethylene and propylene with constant pressure) in the presence of the catalyst and diluent in a reactor, with thorough mixing, and under copolymerization conditions, including means for controlling the reaction temperature to between about 0 and 80xc2x0 C. In particular, the polymerization may be carried out under batch conditions, such as in an inert gas atmosphere and in the substantial absence of moisture. Preferably, the polymerization is carried out continuously in a typical continuous polymerization process with inlet pipes for monomers, catalysts and diluents, temperature sensing means, and an effluent overflow to a holding drum or quench tank. The overall residence time can vary, depending upon, e.g., catalyst activity and concentration, monomer concentration, reaction temperature, monomer conversion and desired molecular weight, and generally will be between about thirty minutes and five hours, and preferably between about 1 and 2 hours.
The resulting copolymers typically would be weighed and analyzed by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) to determine the monomer conversion, copolymer composition, thermal transition temperature and molecular weight, respectively.
The extent of double enchainment can be quantified by 1H NMR spectrum to determine the unsaturation/divinylbenzene (TUS/DOU) ratio of the copolymer. Thus, for a linear copolymer of the Formula (I), without any double enchainment at the incorporated divinylbenzene units, a 1H NMR spectra would show four chemical shifts near 5.3, 5.8, 6.8 and 7.0-7.4 ppm (with the integrated peak intensity ratio=1:1:1:4), corresponding to three individual vinyl protons and four aromatic protons in the pending styrene unit. One can also observe a small peak at 4.7 ppm in low molecular weight copolymers, due to the terminal vinyl group at the chain end. In most high molecular weight copolymer cases, the terminal vinyl group is less than 10% of the vinyl groups derived from divinylbenzene units. Therefore, the ratio of unsaturation/divinylbenzene (TUS/DOU) in the linear alpha-olefin copolymers of this invention is always near unity (typically from about 0.8 to 1.1). A significant deviation of this peak intensity ratio from unity indicates the extent of double bond enchainment in the incorporated divinylbenzene units, which results from branching and/or crosslinking in the copolymer. As will be seen in the examples hereinbelow, a good correlation was observed between the reduction of TUS/DOU ratio and the reduction of copolymer processibility (solubility), due to the presence of crosslinking in certain copolymers. In further connection with TUS/DOU ratios, it will be appreciated that a high TUS/DOU ratio (considerably higher 1) will be observed for low molecular weight copolymers, which do not have any divinylbenzene units and have only a terminal vinyl group. On the other hand, a low TUS/DOU ratio (considerably lower than 1) would be observed if a significant portion of the divinylbenzene units incorporated in the copolymer engaged in double enchainment to produce a copolymer having a long-chain branched structure.
One major advantage of the alpha-olefin and divinylbenzene copolymers (I) is the existence of numerous pendant styrene groups along the backbone. The pendant styrene groups are very reactive in many chemical reactions, including free radical, cationic, anionic and transition metal coordination reactions, and can serve as the reactive sites for selective functionalization reactions to produce functionalized polyolefins, or they can serve as the monomers, initiators and chain transfer agents for subsequent graft reactions which produce polyolefin graft copolymers having polyolefin backbone and other polymer side chains. It will be apparent that the reactivity of the functionalized copolymers enables subsequent derivatization reactions to considerably broaden the copolymer composition and structures that can be achieved.
The functionalized polyolefins and graft copolymers of the present invention may be represented by the Formula (II), illustrated below: 
in which R is defined above in connection with Formula (I). G and Gxe2x80x2, independently, are selected from xe2x80x94H, xe2x80x94OH, epoxy, xe2x80x94NH2, xe2x80x94COOH, anhydride, xe2x80x94Cl, xe2x80x94Br, xe2x80x94M, xe2x80x94COOM (M=metal, e.g. Li, Na, K and Ca) or a polymer chain having a molecular weight of at least about 500, which can be derived from both step and chain polymerization reactions; x and y are as previously defined in connection with Formula (I); m is the mole % of divinylbenzene units remaining in the functionalized copolymer; n is the mole % of functionalized styrenic units and is at least 0.05% (preferably at least 0.1%); and the sum of x, y, m and n is 100%. As indicated in connection with Formula (I), the combined alpha-olefin mole % (x+y) in the functionalized copolymer (Formula (II)) is between about 50 to 99.09%. Preferably, x+y is greater than 60% and is from 85 to 99.9%, and most preferably x+y is from 95 to 99.9%. The backbone polymer chain (Formula (I)) has a number average molecular weight (Mn) of at least about 1,000, and preferably at least about 10,000.
The functionalization reactions of alpha-olefin/divinylbenzene copolymer (I) involve conventional organic olefinic chemistry, which can be run in bulk, finely dispersed slurry solution, or homogeneous polymer solution. Usually, bulk reactions also can be effective in an extruder, or other internal mixer, suitably modified to provide adequate mixing. The details of such bulk processes are set forth, for example, in U.S. Pat. No. 4,548,995, the disclosure of which is incorporated herein by reference. Solution processes are advantageous in that they permit good mixing and an ability to control reaction conditions more easily. Solution processes also facilitate the removal of undesired by-products. A disadvantage of solution processes is the need for removing residual unreacted divinylbenzene prior to chemical modification reactions.
Some resulting functional polyolefins contain several pendant functional groups, such as xe2x80x94OH, epoxy, xe2x80x94NH2, xe2x80x94COOH, anhydride, xe2x80x94Cl, xe2x80x94Br, that are very reactive in subsequent coupling reactions with a polymer having a terminal reactive group to form graft copolymer (II). The coupling reaction can be carried out in solution or melt, and it can be accomplished during a reactive extrusion process. One example of such a coupling reaction is the reaction between a polyolefin (such as PP) containing pendant succinic anhydride groups and a polyamide (such as Nylon 6) having a terminal xe2x80x94NH2 group. The resulting PP-g-Nylon contains phenylsuccinimide linkages between two types of polymer chains. Another example of the coupling reaction is the reaction between a polyolefin (such as PE) containing pendant succinic anhydride groups and a poly(ethylene glycol) methyl ether having a terminal xe2x80x94OH group. The resulting PE-g-PEO graft copolymer contains phenylester linkages.
In preferred aspects of the invention, the pending styrene moieties in alpha-olefin/divinylbenzene copolymers (I) serve as monomer, initiator, and chain transfer units in a subsequent graft reaction with other olefinic monomers. The graft reactions include graft-from, graft-onto, and graft-through processes. The pendant styrene moieties, resemble a styrene monomer in that they are very reactive in many chain polymerization reactions, including free radical, cationic, anionic and transition metal coordination polymerization reactions. In the presence of olefinic monomers, alpha-olefin/divinylbenzene copolymers (I) and catalyst, a graft polymerization reaction takes place involving the pendant styrene groups in the alpha-olefin/divinylbenzene copolymer to form the graft copolymer (II). Most graft reactions take place in homogeneous solution or finely dispersed slurry solution.
In the case of an anionic graft reaction, the preferred process involves the conversion of pendant styrene groups to living anionic initiators, which would begin with a metallation reaction of copolymer (I) with alkyllithium (such as n-BuLi) to form a polyolefin containing pendant benzylic anions, as illustrated below. 
By limiting the amount of alkyllithium added to the reaction to an amount less than would be required to react with all of the divinylbenzene units in the copolymer (I), the metallation reaction between styrene and alkyllithium will be quantitative. In other words, no purification will be needed before adding an anion-polymerizable monomer to continue the living anionic graft-from polymerization process. Preferred anion-polymerizable monomers include, for example, vinyl aromatic compounds, such as styrene and alkyl substituted styrene, acrylamides, alkyl acrylates and methacrylates, and conjugated dienes, such as isoprene and butadiene, and their mixtures. With the coexistence of polymeric anions and monomers susceptible to anionic polymerization, living anionic polymerization takes place, as is described, for example, by R. Milkovich et al in U.S. Pat. No. 3,786,116. It is important to note that the anionic polymerization of various monomers, such as methyl methacrylate, can take place at room temperature without causing any detectable side reactions, which may be associated with the stable benzylic anion initiator. After achieving the desired composition of the graft copolymer, the graft-from reaction can be terminated by adding a proton source, e.g., an alcohol such as methanol or isopropanol, or other conventional polymerization terminator to the reaction mass. In addition, the living anionic chain ends can be converted to a variety of functional groups by controlled termination reactions using any of a number of electrophiles, including ethylene oxide, propylene oxide, episulfides and carbon dioxide, before adding the proton source. The termination reactions are very effective at room temperature. However, a slight molar excess of the terminating agent usually is used to assure complete termination of the polymerization reaction. A wide range of polymers, including random and block copolymers, with well-defined molecular weight and narrow molecular weight distribution, can be prepared by anionic polymerization. Thus, by using this easily controllable living graft-from reaction technique, a variety of graft copolymer compositions with well-defined side chain segments have been produced.
In the transition metal coordination graft reaction process, the pendant styrene units in the alpha-olefin/divinylbenzene copolymers (I) serve not only as monomers in the graft-through reactions but also as chain transfer agents in the graft-onto reactions as illustrated below. 
After mixing the copolymer (I) and an olefin monomer with or without hydrogen in a suitable diluent, the transition metal coordination catalyst is then introduced to initiate graft-through or/and graft-onto polymerization reactions. Olefin monomers that may be used include, for example, aliphatic alpha-olefins, aromatic vinyl compounds, cyclic olefins, and their mixtures having 2 to 15 carbon atoms. Suitable aliphatic alpha-olefins include, for example, ethylene, 1-propene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, and so on. Suitable aromatic vinyl compounds include, for example, styrene and styrene derivatives, such as p-methylstyrene, p-chlorostyrene or the like. Suitable cyclic olefins include, for example, norbornene and norbornene derivatives, such as 1-methylnorbornene, 5-methylnorbornene, 5,6-dimethylnorbornene or the like. Suitable diluents include the general group of aliphatic and aromatic hydrocarbons, used singly or in a mixture, such as propane, butane, pentane, cyclopentane, hexane, toluene, heptane, isooctane or the like.
The transition metal coordination catalysts capable of olefin polymerization may be used for the graft reaction. Catalysts of this type include the active ionic complex shown in the following formula: 
wherein L is a ligand such as cyclopentadienyl, substituted cyclopentadienyl, amido, phosphido, a bulky alpha-diimine group or the like, or a bridged ligand having a covalent bridging group (such as silane, methyl and dimethyl groups) between two ligands; X is selected from hydride, halo, alkyl, aryl, aryloxy, and alkoxy; m and n, independently, are 0, 1 or 2; R1 is a hydride or hydrocarbon having from 1 to 20 carbon atoms; and p is 1 or 2. M is a transition metal of Groups IIIB to VIIB and VIII of the Periodic Table. Particularly suitable catalysts are metallocene complexes of a Group IVB and VB metal such as titanium, zirconium and hafnium. Axe2x88x92 is a non-coordinating, compatible anion. Particularly suitable anions are those derived from methylaluminoxane (MAO) and borates, such as tetra(pentafluorophenyl)borate and methyltri(pentafluorophenyl)borate. The ionic catalyst species useful in the invention may be prepared by methods known in the art. For example, they may be prepared by combining (a) a transition metal compound of the Groups IIIB to VIIB and VIII of the Periodic Table and (b) a compound capable of reacting with a transition metal compound to form an ionic complex. In the reaction of compounds (a) and (b), the compound (a) forms a cation formally having a coordination number that is one less than its valence, and the compound (b) becomes a non-coordinating, compatible anion.
The graft polymerization processes of the present invention can be carried out under homogeneous or suspension solution conditions, depending on the copolymer (I) and olefin monomer used.
The hydrogen gas provides a vital role in the graft-onto reactions, especially using iso-specific metallocene catalysts (such as rac-SiMe2[2-Me-4-Ph(Ind)]2ZrCl2/MAO complex) that engages the polymerization of propylene and styrene with 1,2- and 2,1-insertion modes, respectively. The detailed reaction mechanism is illustrated below. 
During the polymerization of propylene (with 1,2-insertion manner) the propagation Zrxe2x80x94C site (Ixe2x80x2) can also react with the pendant styrene unit (with 2, 1-insertion manner) in the copolymer (I) to form a dormant propagating site (IIxe2x80x2). Although the catalytic Zrxe2x80x94C site in compound (IIxe2x80x2) becomes inactive to both propylene and styrene, due to a steric jamming during the consecutive insertion of 2,1-inserted styrene and 1,2-inserted propylene (see Chung et al, J. Polym. Sci. Polym Chem., 37, 2795, 1999), the dormant Zrxe2x80x94C site (IIxe2x80x2) can react with hydrogen to form the desirable graft copolymer (II) and regenerate a Zrxe2x80x94H species that is capable of reinitiating the polymerization of propylene and of continuing the polymerization cycles. The molecular weight of PP graft is linearly proportional to the molar ratio of [propylene]/[pendant styrene units], and basically independent of the [propylene]/[hydrogen]. However, hydrogen is crucial to maintain high catalyst activity.
In the free radical graft reaction process, the pendant styrene units in the alpha-olefin/divinylbenzene copolymer (I) serve as monomers directly. After mixing the copolymer (I) with the free radical polymerizable alpha-olefin monomer in a suitable diluent, the free radical initiator is introduced to initiate graft-onto or/and graft-through polymerization reactor under conditions effective to form free radicals. As the radical polymerizable monomer to be used in this graft reaction, those well known in the art can be used. Specific examples of suitable monomers include methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacylate, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, 2-hydroxyethyl acrylate, glycidyl acrylate, acrylic acid, maleic anhydride, vinyl acetate, acrylonitrile, acrylamide, vinyl chloride, vinyl fluoride, vinylidenedifluoride, tertrafluoroethylene, styrene, alpha-methyl styrene, trimethoxyvinylsilane, triethoxyvinylsilane and so on. These radical polymerizable monomers can be used either singly or as a combination of two or more monomers.
In a thermal initiation process, the reaction temperature may be in the range of 50 to 250xc2x0 C., preferably in the range of from 65 to 120xc2x0 C. The polymerization time typically is in the range of from about 10 minutes to about 30 hours, and preferably from about 1 to 15 hours.
The following examples are illustrative of the invention.